Device for increasing crankcase compression in an internal combustion engine

ABSTRACT

A device for increasing crankcase compression in an internal combustion engine. The device includes a holder having an annular peripheral wall joined to an end wall. The holder is mounted on a crankshaft of the engine, between a main bearing and a crank portion with a counterweight. The crankshaft extends through the end wall and is surrounded by the peripheral wall. Lightweight filling bodies are disposed in the holder.

BACKGROUND OF THE INVENTION

The present invention relates to a device for increasing crankcasecompression in an internal combustion engine, said engine comprising acrankshaft having main bearings and at least one crank portion includinga counterweight, and filling bodies forming an annular unit togetherwith said crank portion.

It is previously known that the performance of a two-cycle engine can beimproved by increasing the crankcase compression, which can be achievedby reducing the volume of the crankcase. To this end it has beenproposed to use various types of lightweight filling bodies attached tothe crank portion of the crankshaft. Such a filling body is preferablyshaped so as to form an annular unit together with the crank portion.The disadvantage of such known devices is that the manufacture andmounting thereof are relatively complicated and costly and they havetherefore not been used to any great extent.

Although the device according to the invention is primarily intended tobe used in two-cycle engines, it may also be applicable in four-cycleengines, namely such engines of the type using crankcase scavenging forthe purpose of lubrication by fuel mixed with lubricating oil. Suchfour-cycle engines may be used for example in tools having greatlyvarying angular working positions preventing the use of a normalpressurized lubrication system. The invention is therefore notrestricted to two-cycle engines.

SUMMARY OF THE INVENTION

According to the invention, a device for increasing the crankcasecompression has been provided which is uncomplicated in manufacture andcan thus be produced at low cost. Another advantage is that the devicecan be easily mounted in the engine and is consequently well adapted torational series production. A further advantage is that no alteration ofthe crankshaft is required, and neither is any costly modification ofother parts of the engine.

The above advantages have been achieved by means of a device of the kindmentioned in the introduction which according to the invention isgenerally characterized in that the filling bodies are provided in aholder comprising an annular, peripheral wall adapted to surround saidcrank portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following withreference to the accompanying drawings, in which

FIG. 1 is a perspective view of a preferred embodiment of the deviceaccording to the invention,

FIG. 2 is a front plan view on a larger scale of the device shown inFIG. 1,

FIG. 3 is a rear plan view on a larger scale of the same device,

FIG. 4 is a sectional view along line IV--IV in FIG. 3, and

FIG. 5 is a perspective view of a crankshaft provided with the deviceaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the device shown in the drawings comprises acup-shaped, cylindrical holder 10, preferably made of metal, such assheet steel or light metal, or reinforced plastic, such as glass fiberreinforced polyamide. The holder 10 comprises a peripheral, cylindricalwall 10a, and a plane end wall 10b, said last mentioned wall having acentral opening 10c for receiving a crankshaft 11. As is best seen inFIGS. 2 and 3, the end wall 10b has recesses 10d for providing gascommunication as will be described below. The cylindrical wall 10a has adiameter adapted to surrounding the crank portion 12 of the crankshaftwith a suitable fit, and the crank portion has a counterweight 13, as isconventional. The holder is furthermore provided with filling bodies 14,15 having a shape corresponding to the space between the crank portion12 and the peripheral wall 10a. In order to minimize the influence ofthe filling bodies on the balance of the crankshaft the filling bodiesare made of a lightweight material such as glass fiber reinforcedplastic, or a light metal such as aluminium or magnesium. The fillingbodies can be made as hollow shells, or as homogeneous bodies oflightweight material.

For attaching the filling bodies to the holder 10 the end wall 10b isprovided with two depressions 16, 17, each having two openings 18, 19,respectively. During manufacture the filler bodies 14, 15 are molded insitu in the holder 10, the material filling also the openings 18, 19 andthe depressions 16, 17, as shown in FIG. 4. The filling bodies arethereby permanently attached to the holder 10. As an alternative, thefilling bodies and the holder may be made integral, either of lightmetal by for example die casting, or of above-mentioned plastic materialby injection molding or vacuum forming.

The crankshaft 11 shown in FIG. 5 is of a conventional type providedwith two crank portions 12 and a connecting rod 20 connected thereto.Each of the crank portions is provided with a device according to theinvention. The crankshaft is rotatably journalled in a crankcase (notshown) by means of two main bearings 22, 23. As can be seen in theFigure, the holders 10 are mounted on the crankshaft between therespective main bearing and crank portion and are thereby held in placein the correct position without the need for any special attachmentmeans. In order to achieve correct fixing of the device without play thedistance between the main bearing and the crank portion is adapted tothe thickness of the wall 10b. Sufficient lubrication of the mainbearings is ensured by the recesses 10d of the end wall, through whichfuel/oil mixture is supplied to the main bearings during operation ofthe engine.

It is also within the framework of the invention to attach the holder 10to the crank portion by other methods. For example, the peripheral wall10a could surround the crank portion by a suitable press fit. In anothermodification, the end wall 10b could have another configuration than theshown plane shape, or could be omitted entirely, the filling bodiesbeing instead attached to the peripheral wall 10a. Such attachment canbe made as described above, or the filling bodies can be made integralwith the holder. It should also be clear that the volume of the fillingbodies can be modified according to the desired performance of theactual engine and need thus not have the generally maximum volume shownin the drawings.

I claim:
 1. A device for increasing crankcase compression in an internalcombustion engine, said engine comprising a crankshaft (11) having mainbearings (22, 23) and at least one crank portion (12) including acounterweight (13), and filling bodies forming an annular unit togetherwith said crank portion, wherein the filling bodies (14, 15) areprovided in a holder (10) comprising an annular, peripheral wall (10a)adapted to completely surround said crank portion, said holder beingdisposed between one of said main bearings and said crank portion, andsaid filling bodies having a shape corresponding to the space betweenthe crank portion and the peripheral wall.
 2. Device according to claim1, wherein the holder (10) comprises an end wall (10b) connected to theperipheral wall (10a) and having a central opening (10c) for receivingthe crankshaft (11).
 3. Device according to claim 2, wherein at leastone axial passage (10d) is formed in the end wall, said axial passageallowing a flow of fuel mixed with lubricating oil to flow therethroughto lubricate the main bearing.
 4. Device according to claim 1, whereinthe filling bodies (14, 15) are made of reinforced plastic.
 5. Deviceaccording to claim 1, wherein the filling bodies (14, 15) are hollow. 6.Device according to claim 1, wherein the filling bodies (14, 15) arehomogeneous.
 7. Device according to claim 1, wherein the filling bodies(14, 15) are made integral with the holder (10).
 8. Device according toclaim 7, wherein the filling bodies (14, 15) and the holder (10) aremade of reinforced plastic by injection molding or vacuum forming. 9.Device according to claim 7, wherein the filling bodies (14, 15) and theholder (10) are made of light metal by die casting.
 10. Device accordingto claim 1, wherein the filling bodies (14, 15) and the holder (10) aremade of reinforced plastic by injection molding or vacuum forming. 11.Device according to claim 1, wherein the filling bodies (14, 15) and theholder (10) are made of light metal by die casting.
 12. Device accordingto claim 1, wherein the holder (10) is attached to the crank portion(12) by a press fit.